The present invention relates to a method for measuring a surface temperature of a sensor, and more particularly to such a method employing an electrical heating method for measuring various physical properties of fluids.
Generally, it is very important for a process control of a fluid to measure physical properties of the fluid (for example kinematic viscosity).
In Japanese Patent laid-open application 60 (1985)-152,943, there is disclosed a method for measuring physical properties of a fluid by using a thin metal wire as a sensor by putting the thin metal wire into a fluid as a measuring object, charging the thin metal wire with electricity so as to add heating to the sensor and then calculating a heat transfer coefficient on the surface of the thin metal wire.
In the above mentioned method, because a heat-transfer coefficient is calculated from the function of a surface temperature of a sensor, the precise measurement of a surface temperature of a sensor is of great importance.
Recently, various kinds of sensing devices have been used. Especially, the abovementioned thin metal wire sensors have difficulties in the durability and the strength.
Thus a multiple layer sensor coated with an insulated membrane on the surface of a thin metal wire has been employed to improve that durability and strength.
However, in the prior art, no method has been known for precisely measuring a surface temperature of such a multiple layer sensor without direct contact of a temperature sensing device to the surface of the multiple layer sensor. This contact with the temperature sensing device will, however, result in the usual significant changes of the surface temperature of the multiple layer sensor and, of course, give false measurements.